Most semiconductor devices require an electrical contact for receiving electrical charge. Such a contact typically includes an upper "bonding" layer of metal that is in electrical connection with a wire that delivers the electrical charge. The bonding layer is also in electrical connection with a "cap" layer of the semiconductor device. The cap layer is formed from semiconductor material, and is in electrical contact with underlying semiconductor device layers. In that manner, electrical charge is delivered to the semiconductor device.
The electrical contact creates a metal (bonding layer)/semiconductor (cap layer) interface. The contact is identified as "ohmic" when electrical charge (i.e., electrons) is free to move across the metal-semiconductor interface.
Semiconductor device performance and reliability depend, in large part, on the "quality" of the interface or contact. Instability in prior art ohmic contacts (actually, in the metal layers serving as the contact to the semiconductor materials) has been associated with semiconductor device degradation. Such instability is caused, at least in part, by the tendency of the various layers of the ohmic contact to chemically react, over time, with one another.
A need therefore exists for an improved ohmic contact having substantially no tendency for continued reaction after the contact is formed.